Discussion

Anomalous origin of the left coronary artery from pulmonary artery is a rare entity affecting 1/300,000 live births; ^{Reference Boutsikou, Shore and Li1,Reference Chattranukulchai, Namchaisiri and Tumkosit4} 90% die in infancy if undiagnosed but a subset may survive into adulthood. ^{Reference Chattranukulchai, Namchaisiri and Tumkosit4} Two primary mechanisms of survival into adulthood have been described; well-formed inter-coronary collaterals perfusing the left ventricular myocardium or presence of high pulmonary artery pressures allowing antegrade flow into the left coronary artery. ^{Reference Peña, Nguyen, Merchant and Dennie5,Reference Qiu, Yang and Wang6} Clinical presentation in adulthood typically entails angina, myocardial infarction, exertional dyspnoea, or sudden cardiac death. ^{Reference Qiu, Yang and Wang6,Reference Dilaveris, Koutagiar, Alexopoulos, Tsiachris and Gatzoulis7} The latter could be the first presentation accounting for 90% of cases presenting beyond infancy. ^{Reference Yau, Singh, Halpern and Fischman2,Reference Alexi-Meskishvili, Berger, Weng, Lange and Hetzer3}

Our patient presented 2 months peri-partum with witnessed aborted cardiac arrest, leading to timely diagnosis. The presence of an ischaemic aetiology and a surgically correctable lesion excluded the differential diagnosis of peri-partum cardiomyopathy. Successful prompt resuscitation enabled appropriate surgical correction. Intraoperative pulmonary artery pressures were normal without any epicardial inter-coronary macro collaterals. This enigmatic presentation and survival into adulthood highlight the potential role of microvascular collaterals as another mechanism of survival.

The chronology of clinical presentation was also significant. Haemodynamic changes during pregnancy and delivery could have precipitated myocardial dysfunction in the setting of chronic subendocardial ischaemia. During pregnancy, an increase in blood volume, cardiac output, and heart rate occur with a decrease in both systemic and pulmonary vascular resistance. Pregnant women are susceptible to pulmonary oedema given reduction in the colloid osmotic pressure/pulmonary capillary wedge pressure gradient. ^{Reference Soma-Pillay, Nelson-Piercy, Tolppanen and Mebazaa8} Patients with anomalous origin of the left coronary artery from pulmonary artery appear to be even more susceptible due to shifting of blood away from higher pressure coronary circulation to lower pressure pulmonary circulation causing coronary steal. This, along with increased cardiac workload can contribute to ischaemia and cardiomyopathy. Although the differential diagnosis with this presentation can include peripartum cardiomyopathy, a thorough investigation must be done to elicit the underlying pathology. Echocardiogram revealed left ventricular dysfunction, but cardiac MRI confirmed the diagnosis, emphasising the role of multimodality imaging in anomalous origin of the left coronary artery from pulmonary artery.

While echocardiography is instrumental to diagnosis in infancy, cardiac MRI is more useful in adults providing information on myocardial perfusion, fibrosis, and viability. ^{Reference Kim, Cho, Hwang and Nah9} Restoration of a dual coronary system will prevent further ischaemia and arrhythmias, but not alter the underlying substrate for malignant ventricular arrhythmias. Delayed enhancement on cardiac MRI and history of aborted cardiac arrest established class I candidacy for Implantable Cardioverter Defibrillator for secondary prevention. Surgical myocardial revascularization is the standard of care recommended by the American Heart Association for Adult Congenital Heart Disease treatment guidelines. ^{Reference Stout, Daniels and Aboulhosn10}

A high index of suspicion for anomalous origin of the left coronary artery from pulmonary artery should be maintained in patients presenting with ischaemic cardiomyopathy in the pregnant/post-partum patient. Our case reiterates knowledge gaps in mechanisms leading to survival into adulthood and highlights the role of multimodality imaging to assess both functional and anatomical cardiac reserve.